JPH03235371A - Method for manufacturing tandem solar cells - Google Patents

Abstract

PURPOSE:To enable a solar battery of III-V group semiconductor developing less lattice defects on a silicon substrate to be formed for increasing the photoelectric conversion efficiency by making the surface of the silicon substrate porous for a silicon solar battery. CONSTITUTION:A single crystal silicon solar battery is composed of an n-silicon layer 1 and a p-silicon layer 2. Next, the substrate surface of said solar battery is anodized in fluoric acid solution making the surface porous to form a porous silicon layer 3. Next, an n-GaAs layer 4 and a p-GaAs layer 5 are formed on the layer 3 to manufacture the title tandem type solar battery. The photoelectric conversion efficiency of this solar battery is measured to be 27% so that the higher conversion efficiency than that of 24% of the solar battery formed by conventional process may be attained. That is, a compound semiconductor subject to less transposition and residual stress can be grown by making the topmost surface of a silicon substrate porous thereby enabling a high performance solar battery to be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a tandem solar cell, and particularly relates to a method for manufacturing a tandem solar cell, in which a solar cell of a ■-V group compound semiconductor is stacked on a silicon solar cell. The present invention relates to a method for manufacturing a solar cell.

[Prior Art] As a solar cell exhibiting high photoelectric conversion efficiency per unit area, there is a tandem solar cell in which solar cells having different forbidden band widths are stacked. For such solar cells,
Tandem solar cells are known in which an AlGaAs solar cell is stacked on a GaAs solar cell.

[Problems to be Solved by the Invention] However, such conventional tandem solar cells are not suitable for solar cells that require extremely high conversion efficiency per unit area, such as solar cells used in outer space. The conversion efficiency was low and still insufficient. It has been reported that a silicon solar cell stacked with an m-v group compound semiconductor solar cell such as GaAs has an expected conversion efficiency of 38%, which shows higher conversion efficiency. There is. However, in such a battery structure, it is necessary to grow a compound semiconductor, which is a different material, on a silicon substrate, and in order to obtain good crystals, conditions and methods different from normal growth methods are required. For example, when growing GaAs on a silicon substrate, an off-angle silicon substrate is used, or a two-step growth method including thermal cleaning at the temperature of the silicon substrate and a low-temperature growth layer is used.

Furthermore, methods such as introduction of an intermediate buffer layer, introduction of a strained superphoton layer, thermal cycling during growth, and thermal annealing after growth are being investigated, and these methods have slightly improved crystallinity. However, it is still insufficient. For example, taking the dislocation density as an example, a GaAs substrate using the LEC method has a density of about IQ'cm-2;
In the case of GaAs grown on a silicon substrate, 1×1
06 cm-2, which is a fairly high value.

The purpose of this invention is to solve such conventional problems,
An object of the present invention is to provide a method for forming a solar cell of an m-v group compound semiconductor with few lattice defects on a silicon substrate, which becomes a silicon solar cell.

[Means for Solving the Problems] A method for manufacturing a tandem solar cell of the present invention includes a step of making the surface of a silicon substrate on which an n-layer and a p-layer functioning as a silicon solar cell are formed porous; (1) Forming a solar cell of a group V compound semiconductor on the surface of the silicon substrate.

As a method for making the surface of a silicon substrate porous, for example, there is a method of making the surface porous by anodization in a hydrofluoric acid solution. The thickness of the layer to be made porous is not particularly limited, but it can be made, for example, from several μm to several hundred μm.

The pore diameter of the porous portion is, for example, 20 to 300.
It is about the size of a person.

Examples of the ■-v group compound semiconductor stacked on a silicon substrate include GaAs, GaP, and In.
Binary compound semiconductors such as P, A/GaAs
, AA'GaP, InAlAs5 InAAP, GaA
, sP, GaInP, and other ternary compound semiconductors can be selected. Alternatively, a plurality of these may be laminated.

[Operations and Effects of the Invention] The surface of the porous silicon substrate has, for example, 20
~300 innumerable pores are formed, and the compound semiconductor that grows on these pores grows in a form that bridges the pores, and even if the lattice constants are different, it can grow while alleviating the distortion caused by lattice mismatch. Therefore, the introduction of misfit dislocations can be prevented. Growth on such a porous silicon substrate surface is reported, for example, in Toshimichi Ito and Takehisa Kato, Oyoi Jitsu 57 (1988) 1710.

Furthermore, porous silicon has a Young's modulus that is approximately one-tenth that of normal silicon, making it highly flexible. Regarding this, Barla, R. Herino
, G., Bomchil, J.

C, Pfister and A, Freund, J.

Cryst, Growth 68 (1984) 7
It has been reported on 27. For this reason, even if the combination of ■-V group compound semiconductor and silicon have significantly different coefficients of thermal expansion, the strain in the two materials can be absorbed by the porous layer, preventing dislocations and residual stress in the compound semiconductor layer. can be significantly reduced.

Therefore, by making the outermost surface of the silicon substrate porous, it is possible to grow a single compound semiconductor with less dislocations and residual stress, thereby making it possible to produce a solar cell with higher performance.

[Embodiment] FIG. 1 is a sectional view showing an embodiment of the present invention. Referring to FIG. 1, a single crystal silicon solar cell is composed of an n-silicon layer 1 and a p-silicon layer 2.

The surface of the substrate of this single-crystal silicon solar cell is made porous by anodization in a hydrofluoric acid solution, and a porous silicon layer 3 is formed.
was formed.

n-GaAs on this porous silicon layer 3
A N4 and p-GaAs layer 5 was formed. When the photoelectric conversion efficiency of the solar cell thus obtained was measured, it was 27%. On the other hand, according to the conventional method, G is directly applied onto the silicon substrate without forming the porous silicon layer 3.
The photoelectric conversion efficiency of a solar cell grown with an aAs layer is 24%.
Met.

FIG. 2 is a sectional view showing another embodiment of the invention.

Referring to FIG. 2, a silicon substrate that becomes a single-crystal silicon solar cell includes an n-silicon layer 11 and a p-silicon layer 1.
It is composed of 2. The surface of the p-silicon layer 12 is
Similar to the above example, the silicon layer 13 was made porous by anodizing in a hydrofluoric acid solution to form a porous silicon layer 13. On this porous silicon layer 13, an n-GaAs layer 14, a p-GaAs layer 14, a
-GaAs layer 15, n-AA"0.3 Gao7As layer 16, p AA'o,i Gao7As layer 17, n-
AA'L1.6 Gao4As layer 18, pAlo,t,
A Ga(34As layer 19) was grown and three solar cells were stacked on top of the single crystal silicon solar cell. The photoelectric conversion rate of this solar cell was measured and was 32%.

On the other hand, as a comparison, without making the surface of the p-silicon layer 120 porous, a GaAs solar cell, A10,3G
ao, 7 As solar cells and AI. ,6Gao4As
When the photoelectric conversion rate of the solar cell in which the solar cells were stacked was measured, it was 29%.

As is clear from the above, the solar cells of the Examples according to the present invention all exhibited high photoelectric conversion efficiency, and were found to be high-performance solar cells.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIG. 2 is a sectional view showing another embodiment of the invention. In the figure, 1.11 is the n-silicon layer, and 2°12 is the p-silicon layer.
-Silicon layer, 3.13 is porous silicon layer, 4,14
is n-GaAs layer, 5.15 is p-GaAs layer, 16 is n-AA'o3Gao7As layer, 17 is p-AIo3G
a, 7As layer, 18 is n-AIo6Gao4As layer, 1
9 is pAI. 6Gao, 4As layers are shown. Figure 1

Claims (5)

[Claims] (1) A step of making the surface of a silicon substrate on which an n-layer and a p-layer are formed to function as a silicon solar cell porous, and forming a solar cell of a group III-V compound semiconductor on the surface of the porous silicon substrate. A method for manufacturing a tandem solar cell, comprising a step of forming a tandem solar cell. (2) The method for manufacturing a tandem solar cell according to claim 1, wherein the step of making it porous includes making it porous by an anodization method in a hydrofluoric acid solution. (3) The III-V compound semiconductor solar cell is made of GaA
The method for manufacturing a tandem solar cell according to claim 1, comprising an s-layer. (4) The III-V compound semiconductor solar cell is made of GaA
The method for manufacturing a tandem solar cell according to claim 1, comprising an s-layer and an AlGaAs layer. (5) The III-V compound semiconductor solar cell is made of GaA
The method for manufacturing a tandem solar cell according to claim 1, comprising an s-layer and an AlGaAs layer having two or more types of Al compositions.